Transferring DNS question

Here is my desired scenario that I'd like someone to verify that this will work properly without taking down my existing site.

I have 2 servers, registered with different hosts and running on different platforms.

Server 1 (windows) currently hosts my website and I want to leave that as is.

Server 2 (Linux/cpanel) is new and I want to use it as a mail server for the domain hosted on server 1.

So, in order for the mail server to work i believe i need to register the nameservers with my registrar. First question, will just registering the nameservers have any impact on the domain? My guess is no because I haven't transferred the DNS to server 2 yet. Which leads me to my next question, on server 2, do I just need to point the A record IP for this domain to server 1?

Trying to get server 2 up without server 1 having any downtime as there is traffic hitting the site.

1. No, just registering the nameservers will not affect your domain name.
2. On server 1, all you would have to do is update the A record to the nameserver you registered & set the mail to remote.
ex. mailserver2.yourdomain.com ----> server 2's mail IP address
3. On server 2 just create your email accounts and you're all set.

It's not required to change your name servers if you simply want to modify your MX records. You could keep the control of the DNS for the domain name at the registrar, or you could change it's name servers to ones used by either server. Typically, you want the domain name to use name servers from the server it's hosted on. You should create an account on the second server, so that you can then create the email accounts. Then, ensure you add the proper "A" and "MX" records at the DNS host for the domain name so it's email is directed to the remote mail server.